THE STRUCTURE OF METEORITES 65 



Often the fragments differ enough in color from one another, 

 or from the ground mass, so that the brecciated character is 

 plainly visible to the naked eye. In the stone of Weston, for 

 example, the ground mass is gray, the enclosed fragments 

 blue. In the stone of Siena the angular fragments are of a 

 dark color and the enclosing magma is light colored, while 

 of Bandong, Saint-Mesmin and others the reverse is true. In 

 other meteorites the two components differ chiefly in grain and 

 coherence, as in the meteorites of Jelica, Manbhoom, and Soko- 

 Banja. In these the ground mass is of a somewhat coarse, 

 friable character, while the enclosed fragments are of a dark, fine- 

 grained rock. In regard to the ground mass of other brecciated 

 stone meteorites it may be stated that it may itself be made up 

 of rock splinters, i. e., have a tuffaceous character, or it may be 

 crystalline or half glassy. The half glassy ground mass of the 

 Orvinio and Chantonnay meteorites, as already noted, shows a 

 distinct flow structure around the fragments which it encloses. 



AGGLOMERATED, SANDSTONE-LIKE AND TUFFACEOUS STRUCTURES. 



These may be said to differ from brecciated structure only in 

 the smaller size of the component fragments. The fragments may 

 range from the size of small peas in meteorites of agglomerated 

 structure through that of coarse sand in those which are sandstone- 

 like to that of splinters and fine dust in the tuffaceous meteorites. 

 In the agglomerated meteorites it is often possible to recognize 

 different kinds of rocks. Thus in the Parnallee meteorite Meunier 

 believes he has recognized seven distinct lithologic types. Of the 

 sandstone-like meteorites that of Chassigny is the best example. 

 It is made up of rounded grains of the size of coarse sand. The 

 Shergotty and Ibbenbuhren meteorites are likewise granular in 

 appearance. Not all observers, however, agree that the above 

 are clastic in their origin. The tuffaceous structure is a common 

 one in meteorites, Tschermak, as already noted, regarding prac- 

 tically all stony meteorites as of this nature. The resemblance of 

 these to terrestrial volcanic tuffs is very close, though the stratifi- 

 cation which usually characterizes the latter has never been 



